Time-dependent Density Functional Investigation Research Articles

TDDFT investigation of fluorescence properties of luciferin and oxyluciferin analogs bearing an amino group

Abstract Chemical origin of high chemiluminescence efficiency of firefly luciferin remains an intriguing subject. Developing more efficient fluorescent marked compounds based on the firefly luciferin is in full swing for application in gene expression and gene regulation, and imaging of live tissues fields. Thus, a series of luciferin analogs bearing an amino group of aminoluciferin (AL), quinolylaminoluciferin (QAL), naphthylaminoluciferin (NAL), coumarylaminoluciferin (CAL) and anthrylaminoluciferin (AAL), pyrenylaminoluciferin (PAL) and corresponding keto form oxides were studied in this work, and the ground and excited state properties of them have been calculated by using time dependent density functional (TDDFT) methods in the gas phase, dimethylsulfoxide (DMSO) solution and hydrophobic environment. The results suggested that replacing aminobenzothiazole moiety of firefly luciferin with the larger rigid moieties, the absorption spectra shift to the blue. Bio-heterojunction concept was employed to explain the higher degree of spatial overlap of corresponding orbitals for CAOL, AAOL and PAOL, an important factor to be of beneficial to enhance fluorescence efficiency. In order to further explain the high fluorescence efficiency of CAOL, the process of nonradiative decay is also investigated. Comparing the energy difference of the corresponding singlet and triplet excited states in intersystem crossing and internal conversion, the reasons is qualitatively explained for the high fluorescence efficiency of CAOL. The investigation result for their emission spectra suggested that the emission maximum of AAOL is similar to firefly in nature. The influence of substituent on fluorescent emission was discussed.

The effect of Mn oxidation state on metal core electron excitations in manganese dimers: a time-dependent density functional investigation

Time-dependent density functional theory (TDDFT) calculations have been performed on a series of manganese dimers with averaged metal oxidation states of 2.0, 2.5, 3.0, 3.5 and 4.0. The excitation energies and oscillator strengths of transitions within the Mn K-core edges have been determined. The theoretical edge energies reproduce the experimental correlation between the relative position of the Mn K-edge and the averaged Mn oxidation state extremely well. A comparison with the results obtained previously for Mn complexes with different ligand environments shows that TDDFT can be successfully applied to determine the relative edge energy differences between Mn systems, taking into account the various oxidation states of the metal and differences in ligand environment in a self-consistent manner. The accuracy of the calculated edge energies indicates that the methodology employed in the current study can be used to determine the oxidation states of Mn atoms in the Mn4Ca cluster of photosystem II (PSII).

Linear and Nonlinear Optical Response of Aromatic Amino Acids: A Time-Dependent Density Functional Investigation

The linear and nonlinear optical responses of the three aromatic amino acids tryptophan, tyrosine, and phenylalanine have been investigated by time-dependent density functional theory. The effect of the peptidic chain on the polarizabilities and the first hyperpolarizabilities is addressed by substituting different groups to the chromophores indole, phenol, and benzene. The optimized structures are in very good agreement with the experimental results. Furthermore, the calculated polarizabilities are found to match well with the empirical results, showing the evolution obtained as the chain is lengthened. A systematic and constant increase of the polarizability is found, for the three chromophores, for the various chain lengths. The first hyperpolarizability is also noticeably modified by the chains, but the evolution of this quantity is found to be more dependent on the system considered. Finally, it is suggested that each of the three aromatic amino acids has a significant contribution to the nonlinear response of proteins.

Time dependent density functional investigation of the near-edge absorption spectra of V2O5

We have performed Time Dependent Density Functional Theory (TDDFT) calculations employing a cluster model of the core excitation spectra of vanadium pentoxide, V(2)O(5). The excitation energies and dipole transition moments are determined for all the core edges, vanadium and oxygen K- and vanadium L-edges, treating them at the same level of accuracy. The agreement between the TDDFT theoretical spectra and the experimental data is rather good, particularly at the V and O K-edges. A quantitative reproduction of the fine pre-edge structures appears more difficult for the V L-edge. The comparison between the TDDFT results and the results obtained at the simpler one electron Kohn-Sham (KS) level indicates that the V and O K edges can be correctly described within a single particle approximation (KS), while the strong modification of the V L-edge structures from the KS to the TDDFT description emphasizes the importance of configuration mixing to treat the metal 2p excitations. The origin of the calculated pre-edge features is analyzed in detail with the help of the atom-projected density-of-states of the unoccupied levels. This analysis emphasizes the V 3d dominant character of the final states in the conduction band, probed by the V L-absorption. The strong octahedral distortion of the V(2)O(5) structure allows the mixing of the 3d state with the V 4p components, which are mapped by the oscillator strength in the V K-edge spectrum. The high intensity of the O 1s transitions reflects the presence of a significant O 2p component in the conduction band.

Time-dependent density functional investigation on electronic spectra of 4′- N-dimethylamino-3-hydroxyflavone

The lower singlet excited states for 4′- N-dimethylamino-3-hydroxyflavone (DMA3HF) have been investigated. Theoretical calculations have been performed by using time-dependent density functional theory. The B3LYP and MPW1PW91 functionals with 6-31G(d,p) basis set have been used to compute transition energies. Ground-state geometries are optimized by using density functional theory with both B3LYP and MPW1PW91 functionals combined with 6-31G(d,p) basis set. The first excited state geometries are optimized by using configuration interaction all single-excitations methods with 6-31G(d,p). Vertical absorption energy and excited state electronic dipole moments calculations show that the singlet excited states S 1 of the normal of DMA3HF has the character of a large charge separation and effective charge transfer. Calculated emission energies for both the normal and tautomer show a large Stokes shift between the absorption and fluorescence maxima. The present calculations suggest that DMA3HF appears dual fluorescence in gas phase. Our results obtained explain the strong ‘dual-fluorescence’ feature that involves the excited-state intramolecular proton transfer and charge transfer of DMA3HF.

Dramatic response effects in the photoionization of the second-row hydrides: A time-dependent density functional investigation

Cross section and asymmetry parameter profiles for the ionizations of the valence and core shells of the second-row hydrides have been calculated by the time-dependent density functional theory (TD-DFT) and Kohn–Sham (KS) schemes. The importance of the screening effects has been pointed out by the comparison of the KS and TD-DFT results and has been analyzed in detail for the HCl molecule. The results have been discussed with respect to the nature of the ionized orbitals along the series in order to assess the observed trends. This behavior of the Cooper minima in the outer valence molecular orbitals has been considered in detail both in the cross section and asymmetry parameter profiles. The TD-DFT results, compared with the experimental data, show quantitative agreement with the experiment for the outer-valence and core ionizations. A deterioration of the quality of the TD-DFT results is still present in the inner-valence region.